There are differences in "flint"--a variety of chert to a mineralogist. Cherts can have different microcrystalline sizes, vary in porosity and composition [flint/chert is dominantly silica (SiO2) but can have impurities]. These mineralogical factors can affect how it cuts steel, although hardness is generally ~7 [Mohs scale]. For example, Arkansas Novaculite--a form of bedded chert used as whetstones, tools and "flints"--comes in "grades" that reflect porosity mostly--the smooth translucent white to black stones are ultra dense and impart more of a polish than a cut to steel, whereas the Washita grade has enough porosity to form a "grainy" surface of sharp edges around micropores and these more aggressively cut steel. The other factor is form of the rifle flint per se, that is how it is knapped--its final used form. A smooth front edge will shave off smaller bits of steel from the frizzen I imagine, from microserrations along its edge, whereas a jagged front edge might take off fewer but larger bits of the frizzen--gouge it, as it were. I suspect that frizzen life is affected by such parameters as well as flint life. There are alot of variables in firing a flint lock.
